.alpha.-Aminophosphonic acids represent an important class of organic compounds due to their analogy to .alpha.-aminocarboxylic acids. Indeed, several synthetic derivatives of .alpha.-aminophosphonic acids have pronounced biological activities, including inhibition of proteolytic enzymes and bacterial growth. .alpha.-Aminophosphonic acids also have been found in nature as components of hypertensive active tripeptides. Their biological properties are believed to be strongly influenced by the absolute configuration at the .alpha.-carbon. For example, the L,L-diastereomer of the antibiotic alafosfalin--an .alpha.-aminophosphonate--is considerably more effective than the other three stereoisomers.
Several methods have been devised for preparation of racemic .alpha.-aminophosphonates. However, known asymmetric syntheses are predominantly limited by low to moderate enantiomeric excesses, multiple synthetic operations and little choice of absolute stereochemistry. (See, e.g., Dhawan, et al., Phosphorous and Sulfur 1987, 32, 119) Thus, there is a need for more general synthetic methods that afford aminophosphonates of high optical purity with choice of side chain and absolute stereochemistry.